The present invention is directed, in general, to power systems for subterranean bore hole equipment and, more specifically, to controlling an electrical power drive to prevent damage to subterranean borehole equipment powered by the power drive.
Electrical submersible pump (ESP) systems are frequently employed in the lower portion of a well bore for oil and/or gas producing wells, above or below the casing perforations. ESP pumps are generally employed to pump fluids to the surface or in water flooding for secondary recovery of oil and other hydrocarbon fluids. Normally ESP pumps are driven by downhole motors which are, in turn, powered by three phase power transmitted into the borehole from an electrical drive at the surface.
Various types of electrical drives have been employed or proposed for powering the motor portion of ESP systems, including variable frequency drive (VFD) systems. VFD drives may employ either variable voltage inverter (VVI) or pulse width modulated (PWM) output configurations. While each type of output provides various benefits in use with ESP systems, PWM drives are economical and provide variable speed operation. However, PWM output drives often exhibit voltage spikes and over-voltages as a characteristic of the output voltage waveform, which may result in motor failures and damage to ESPs from contra-rotating torques and other problems, as well as damage to the downhole motor and/or cable insulation. Transmission of stepped-up voltage outputs from PWM output drives over cables of significant length (e.g., anything greater than approximately 2,000 feet) may result in resonance or sequence harmonics for the high frequency carrier signal. Therefore use of PWM drives to drive downhole motors within ESP systems is generally impractical without regulating filter device between the PWM drive output and the step-up transformer (if any).
During operation, however, filters employed for PWM drive outputs being transmitted downhole may fail (from an internal capacitor failure or a fuse blowing within the filter, for example), thus negating the protection provided by the filter.
There is, therefore, a need in the art for a mechanism for safely utilizing filtered PWM drive output to power an ESP. It would be advantageous for such a mechanism to allow pumping operations by the ESP to continue despite the failure of a filter at the output of the PWM drive.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in downhole production system, a controller for a pulse width modulated electrical drive or a dual-mode, pulse width modulated/variable voltage inverter drive coupled to sensors within a filter at the drive output. Upon detecting failure of the filter or filter components (e.g., a capacitor short or blown fuse) through the sensors, the controller either shuts down the drive or automatically switches the drive operating mode to an output mode which does not require filtering. Damage to the electrical system or downhole equipment from transmission of unfiltered or improperly filtered power may thus be averted upon failure of the filter or a filter component.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9corxe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith, xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, whether such a device is implemented in hardware, firmware, software or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases.